A conventional magnetic position detection device (see International Application Number PCT/JP2013/061871, for example) is provided with a magnetic scale formed from a plurality of magnetic pole pairs, each pair having a width 2λ and including a first magnetic portion and a second magnetic portion that exhibit different magnetic properties and each have a width λ. The pairs of magnetic poles are arranged in a row at equal intervals in periods of the magnetic pole pair width 2λ.
Further, a magnetism sensing device is disposed opposite the magnetic scale via a predetermined air gap. The magnetism sensing device is moved relative to the magnetic scale through a magnetic field formed by the magnetic scale in an arrangement direction of the magnetic scale while maintaining the air gap, and variation in the magnetic field during this relative movement is measured using magnetism sensing elements.
As the magnetism sensing elements, the magnetism sensing device includes a group of first magnetism sensing elements constituted by n (where n is a natural number no smaller than 2) first magnetism sensing elements that are arranged at equal intervals of a magnetism sensing element interval P such that λ=nP. The respective first magnetism sensing elements output measurement results indicating variation in the magnetic field during the relative movement in parallel.
A position calculation circuit calculates a relative position of the magnetism sensing device on the magnetic scale by analyzing output values output by the magnetism sensing device. The position calculation circuit calculates the relative position of the magnetism sensing device on the magnetic scale at a position detection resolution of λ/n by analyzing the output values output in parallel by the n first magnetism sensing elements.